Prince Louis Stars in 6th Birthday Portrait Taken by Kate Middleton as She and William Share Personal Message

The image comes one month after Princess Kate's Mother's Day photo with her children was criticized for being edited

Kate Middleton and Prince William are celebrating their son Prince Louis' sixth birthday with a royal tradition.

The Prince and Princess of Wales' youngest child starred in a new portrait in honor of his birthday on April 23.

The photo was taken by Princess Kate in Windsor in the last few days, PEOPLE understands. It came with a simple message from the proud parents: "Happy 6th Birthday, Prince Louis! Thank you for all the kind wishes today."

Royal fans had been eagerly awaiting the release of an image, as it's customary to see one issued on the eve of their children's birthdays. However, given the current circumstances with Kate undergoing cancer treatment and the family's appeal for privacy, expectations were uncertain.

The couple decided to release the image as a way of thanking well-wishers who have reached out to wish their son a happy birthday, PEOPLE understands.

The photo has not been edited, PEOPLE understands. Last month, Kate controversially edited a photo that had been taken by Prince William to mark Mother's Day in the U.K.

In the sweet snap, Prince Louis smiles directly at the camera while lying on a blanket in the grass, his arms propped up as he flashes a big grin.

Louis and his older siblings, Prince George, 10, and Princess Charlotte, 8, recently returned to school after a few weeks off during the Easter holiday.

Prince William, 41, and Princess Kate, 42, have traditionally released a new photo of their three children — Prince George, 10, Princess Charlotte, 8 and Prince Louis — each year on their birthday. They either tap a professional photographer or Kate, who has called herself an "enthusiastic amateur photographer," has gotten behind the camera to take the portraits on many occasions.

Related: Queen Camilla Calls Her Grandson Louis a 'Handful,' But She Didn't Mean Prince Louis

On March 22, Princess Kate revealed to the world that she was undergoing cancer treatment. In her emotional video message, Kate explained that it had been a shock to both process the news and "manage this privately for the sake of our young family," referring to Prince Louis and his siblings.

"Most importantly, it has taken us time to explain everything to George, Charlotte and Louis in a way that is appropriate for them, and to reassure them that I am going to be okay," she said in the announcement.

Princess Kate's news was released as George, Charlotte and Louis began their Easter vacation from school, enabling them to absorb the news away from the exposure of school and for the family to spend private time together.

Related: Prince Louis Has a Classic Little Brother Moment in New Video with Mom and Siblings — See the Clip Going Viral

With the children returning to the classroom at Lambrook School last week, Prince William returned to public duties with a visit to a food distribution charity on April 18. There, he revealed one of Louis' loves: the game of cricket. The royal dad also hinted that Louis and his siblings like a kid-friendly snack. Volunteer Rachel Candappa told reporters that William "pointed at the food and said, 'That’s spaghetti hoops.' And I asked, 'How do you know about spaghetti hoops?' and he said, 'I’ve got children,' " Candappa recounted.

The picture for Prince Louis' birthday will undoubtedly be deeply scrutinized, coming a month after the family released one of the most discussed royal photos ever. To celebrate Mother's Day in the U.K. on March 10, the family released a new portrait of Princess Kate posing with her three children, marking the first official photo of the royal since her abdominal surgery in January (cancer was later discovered through post-operative tests). But within hours of the snap being published, it was at the center of manipulation claims as parts of it had been doctored and prominent picture agencies like AP and Reuters withdrew the image.

The following day, Princess Kate admitted to editing the shot and apologized for “any confusion."

"Like many amateur photographers, I do occasionally experiment with editing. I wanted to express my apologies for any confusion the family photograph we shared yesterday caused. I hope everyone celebrating had a very happy Mother's Day," she said in a statement shared to social media. The message was signed with a "C" for Catherine, indicating the note came directly from her rather than staff.

A royal source told PEOPLE at the time that Kate made what they called “minor adjustments” to the “amateur, family photograph taken by the Prince of Wales."

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Following Prince Louis' birthday, Prince William and Princess Kate have several milestones in the coming months. The couple will have their 13th wedding anniversary on April 29, which they marked last year by sharing a casual photo together posing on bikes.

Princess Charlotte will soon be marking a birthday of her own when she turns 9 on May 2, while Prince George will turn 11 on July 22.

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